By 18 BBY, the Empire had already corrupted Ilum, draining its resources dry as well as having destroyed entire parts of the planet's surface, as they were harvesting kyber crystals for the Death Star; the destruction was visible even from space. When Jedi Purge survivor Ahsoka Tano returned to the planet, she noted that there were at least two Star Destroyers and a mining ship in orbit around the planet. Chunks of the planet had been carved away, exposing the rock and lava that boiled up from the planet's core.[10]

The Jedi Temple on Ilum remained the last sign of intelligent life on Ilum, but was almost entirely covered by ice. All other bases on Ilum were removed by the Jedi. Ilum became a bigger supplier of kyber crystals when other planets exhausted their supplies.[2]

A year after the Gathering took place, the Galactic Empire was proclaimed. The Empire quickly began strip-mining Ilum, revealing magma bubbling from Ilum's core.[10] The entrance to the Jedi Temple had been destroyed to allow access to the crystalcaves.[2] A massive mining ship, as well as two Imperial Star Destroyers stood watch over the planet to gain its riches.[10]

Ilum was not home to a large amount of people, with just 5,200 sentient inhabitants. Of those 5,200, 45% were support crew, 30% were temporary researchers, 20% were military, and the remaining 5% were other individuals living on-world.[2]

Ilum's main attraction was its Jedi temple, hidden beneath a large cliff of ice. Beneath that temple was the planet's massive complex of crystal caves where a vast quantity of kyber crystals could be found, and the site of the Gathering.[6] The remainder of Ilum's surface was barren, save for canyons and mountains.[2]